The test, which measures a gene fusion product called TMPRSS2:ERG, or T2:ERG, predicted a positive biopsy significantly more accurately than did serum prostate specific antigen (PSA) alone or in combination with other clinical predictors, according to a study led by James B. Amberson, MD, of the laboratory company DIANON Systems in Shelton, Conn.

In a second study presented at the same session here at the Genitourinary Cancers Symposium, the T2:ERG urine test was affirmed to improve accuracy by about 10% over the standard clinical risk predictors (area under receiver-operating characteristic curve 0.75 versus 0.65, P<0.001).

The test primarily picked up clinically significant cancers (about 80%) and for those had 85% to 100% specificity compared with biopsy or prostatectomy, reported John T. Wei, MD, of the University of Michigan in Ann Arbor, and colleagues.

"To me as a clinician, if a new test does detect cancer but does no better than what we currently have -- PSA, age, and DRE [digital rectal exam] findings -- then I don't want to use it, it's a waste of money," Wei said at the session.

The test is prostate cancer specific, much like the PCA3 urine test for prostate cancer developed by the same company and which also had positive results reported here at the conference.

That contrasts with PSA, which has been much criticized as a surrogate for prostate size rather than cancer, leading to overdiagnosis and unnecessary anxiety.

One vocal critic, Otis Brawley, MD, chief medical officer for the American Cancer Society, declared great hope in these new urine tests.

"We need tests to make PSA better," he told MedPage Today, "and we need tests to figure out the cancers that kill versus the cancers that are never destined to kill."

However, one hurdle for the T2:ERG test may be that its target is present in only about half of prostate cancers.

Whether he proves to be right may hinge on the test's performance in distinguishing biologically aggressive tumors, a major challenge in urology.

Wei's group studied a biopsy cohort of 623 men from three institutions and a prostatectomy cohort of 142 from one institution. All of the men had a T2:ERG test on post-DRE urine collected before the prostate procedure.

In the prostatectomy cohort, the urine test predicted high Gleason score (P=0.01), upgrading of Gleason score between biopsy and excision (P=0.03), larger tumor size (P=0.002), and clinically significant disease as determined by a tumor over 1.0 cm in size or with Gleason score of 7 or higher or spread outside the prostate (P=0.004).

Sensitivity ranged from 23% to 37%, whereas specificity results were:

88% to 93% overall for prostate cancer

85% to 95% for clinically significant cancer at biopsy

95% to 100% for clinically significant cancer at prostatectomy

In Amberson's study of 453 men scheduled for prostate biopsy at seven community clinics, post-DRE urine testing had 87% specificity and 39% sensitivity and again correlated with biopsy results (P=0.0001) and high Gleason score (P=0.004).

Although sensitivity was low, Amberson called it consistent with the expected roughly 50% prevalence of the gene fusion the test identifies.

Moreover, the urine test appeared to improve on current clinical models, he said.

Its addition to a model that included serum PSA, the PCA3 urine test, percent free PSA, age, prostate volume, family history, race, and results of DRE and prior biopsy improved the accuracy of prediction to an AUC of 0.754 (95% confidence interval 0.75 to 0.76) from 0.715 without it (95% CI 0.71 to 0.72) and 0.597 for serum PSA alone (95% CI 0.54 to 0.65).

The T2:ERG urine test is not commercially available, and Brawley called it not ready for the market until further validation is completed.

No matter what test is developed, it's going to be expensive in the beginning, Brawley cautioned.

But determining who can safely forgo treatment of indolent cancer could end up saving money in the end, Brawley said.

Researchers on both studies reported conflicts of interest with Gen-Probe, including employment and stock ownership.